Here is an example of such a form without an auto-submit. When you make a selection, you are required to submit the form using the standard submit button:
Although there is no action attached to this form, you can see that it is submitted by the actions of the web browser (i.e. in the first one, no action occurs when you make a selection…in the second, you can see that the form is submitted).
<select name=’myfield’ onchange=’this.form.submit()’>
<noscript><input type=”submit” value=”Submit”></noscript>